1. Field of the Invention
The present invention relates to a TV decoder, particularly to a TV decoder having a demodulator disposed in a graphic card and separated from an ADC.
2. Description of the Prior Art
FIG. 1 is a diagram showing a conventional TV decoder. A tuner 11 receives an RF-band TV signal RFTS and outputs a base-band TV signal BTS to a TV decoder chip 12. The TV decoder chip 12 has an analog-to-digital converter(ADC) 111 receiving the signal RFTS and produces image data bits by sampling the signal RFTS, and a demodulator 112. The image data bits are transmitted through signal DS to the demodulator 112. The demodulator 112 also producing control data bits transmitted through signal CS to the ADC 111. The signal CS carrying the control data bits controls a DC level and gain of the signal DS. Finally, the demodulator 112 produces a video signal VD to be processed by a graphic card 13.
In the previously described TV decoder 12, the ADC 111 and demodulator 112 are disposed on the same chip so that the TV decoder chip 12 is an external device connected to the graphic card 13 by a feature connector (not shown) and the transmission of the bits carried by the signals DS and CS is simply parallel.
However, it is costly to manufacture the TV decoder chip 12 having both of the ADC 111 and demodulator 112 since their manufacture processes are totally different. For the sake of cost, it is better to separate the demodulator 112 from the ADC 111, put it into the graphic card 13 and connect the ADC 111 to the graphic card 13 by the feature connector. Unfortunately, a large number of pins are needed between the ADC 111 and graphic card 13 due to the simply parallel transmission of the bits carried by the signals DS and CS, which is not compatible with the pin number of the feature connector.